Photometric radiation analyzers



March-25, 195 8 M. E. REINECKE 2,827,824

PHOTOMETRIC RADIATION ANALYZERS Filed Jan. 17, 1955 2 Sheets-Sheet 1INVENTOR. ME. REINECKE A T TORNE VS March 25,1958 M. E. REINECKE"$827,824

7 PHOTOMETRIC RADIATION ANALYZERS v Filed Jan. 17, 1955 2 Sheets-Sheet 2F 6 INVENTOR. S 3 VM.E. REiNECKE A T TORNEKS PHOTOMETRIC RADIATIDNANALYZERS Marvin E. Reinecke, Bartlesville, kla., assignor to PhillipsPetroleum (Iompany, a corporation of Delaware Application January 17,1955, Serial No. 482,274

2 Claims. (Cl. 8814) This invention relates to radiation analyzers,particularly those utilizing a beam of radiation directed upon aplurality of radiation-sensitive surfaces. In another aspect, theinvention relates to a difierential refractometer of improvedconstruction.

In the copending application of F. W. Crawford, Serial No. 187,600,filed September 29, 1950, now Patent 2,724,304, granted November 22,1955, entitled, Differential Refractometer, there is disclosed aninstrument wherein a beam of radiation is directed upon a pair ofradiation-sensitive devices or detectors, and the radiation beam isdeflected in accordance with the difference between the refractive indexof a sample fluid and the refractive index of a standard fluid.

As the sample fluid changes composition, a deflection of the beam isproduced which changes the relative amounts of radiation incident uponthe two sensitive devices. By comparison of the signals from thesesensitive devices, an output is obtained which is representative of thecomposition of the sample fluid. If desired, the output can be utilizedto drive a servomotor which deflects the beam in a direction opposite tothe direction of deflection caused by the change in composition of thesample, this mechanism operating until the detector circuit is restoredto a predetermined or balanced condition. In this case, the position ofthe servomotor shaft is representative of the sample composition.

In accordance with this invention, the sensitivity of the describedinstrument is improved by interposing an opaque barrier in the path ofthe radiation beam such that the' radiation normally impinging upon thearea between the detectors is blocked out, as is the radiation directedat the portion of the sensitive surfaces of the detectors adjacent thisintermediate region. This has two important advantages. First, a broadbeam of radiation can be used, thus obviating the necessity for usingseveral focusing devices in the optical system. Second, the higher beamintensity in a narrow band produces a proportionately higher output inthe detector when the beam is deflected.

The provision of an opaque barrier of the character stated is extremelyuseful in diflerential refractometers of the type disclosed in theaforementioned Crawford application, and is also generally applicable toradiation analyzers of any type wherein the radiation beam is deflectedand caused to fall upon a plurality of radiationsensitive devices.

Accordingly, it is an object of the invention to provide an improvedoptical system for instruments utilizing radiation.

It is a further object to provide a differential refractometer ofimproved construction.

It is a still further object to provide a differential refractometerwhich is of low cost, utilizes a minimum number of standard componentsand is accurate and reliable in operation.

Various other objects, advantages and features of the invention willbecome apparent from the following de- Patented Mar. 215, 1?:58

tailed description taken in conjunction with the accompanying drawings,in which:

Figure l is a perspective view of a differential refractometerconstructed in accordance with the invention;

Figure 2 is a detail drawing illustrating a feature of the invention;and

Figure 3 is a top view of the optical system, on an enlarged scale.

Referring now to the drawings in detail, I have shown a radiation source10, such as the filament of an incandescent lamp, the radiation fromthis source being thrown by a lens 11 upon a pair of members 12a, 121),which define a wide slit 12c. By the action of the slit 120, a broadbeam of radiation is produced which passes through cells 13a and 13b ofan assembly 13 and, thence, is reflected by mirrors or prisms 14a, 14bonto a pair of radiation detector units 15a and 15b. Where the opticalsystem of the invention is utilized in a differential refractometer,cell 13a can contain a sample of fluid to be analyzed while cell 13b cancontain a standard fluid. In passing through the assembly 13, therefore,the beam is deviated or deflected to an extent which is proportional tothe difference in indices of refraction of the standard fluid and testfluid. As the composition of the sample fluid changes, the deflection ofthe radiation beam changes in a corresponding manner and varies therelative amounts of radiation falling upon the detectors 15a, 15b which,in the example shown, are photoelectric cells.

' Preferably and advantageously, the outputs of the cells 15a, 15b arefed, in opposition, to an amplifier 16, Figure 1. When the output of thedetectors is equal or, if desired, in a predetermined ratio, the systemis balanced and no output is produced by the amplifier. However, if thebeam is deflected by a change in composition of the sample fluid, thesystem is no longer balanced and an,

output is produced by the amplifier 16 which drives a servomotor 17, therotation of the motor shaft being comsample fluids and, hence,representative of the composition of the sample fluid which is,therefore, indicated directly by the position of the shaft of motor 17.

The composition is indicated directly by an indicator .24 connected bygearing 25 to the motor shaft, and the position of the motor shaft isfurther telemetered to a recorder 26 by gearing 26a and a potentiometerZeb.

Offscale movement is prevented by a stop device including aspring-loaded rod 27 cooperating with a cam 28 on the shaft of motor 17and a cam 29 rotatable with the spur gear 19.

Referring now to Figures 2 and 3, it will be noted that the radiationdetectors 15a, 15b are arranged in closely spaced formation and haveradiation sensitive surfaces and 15d of generally rectangularconfiguration, which are separated by a narrow intermediate slit orregion 156.

In accordance with the invention, a barrier 30 is positioned in the pathof the radiation beam, this barrier being opaque to the radiation anddisposed in fixed position upon the base of the instrument. This barrierintercepts the radiation whch would normally fall upon the intermediateregion 152 between the radiation detectors and also the radiation whichwould otherwise impinge upon the surfaces of the radiation-sensitivesurfaces or elements adjacent this intermediate region 15e. Inparticular, where the radiation is in the form of a broad beam, asdescribed, the barrier 30 blocks off the central part of the beam sothat only narrow ribbons, indicated V barrier wasslightlynmore thanone-half inch wide so that the ribbons of'radiation impinged upon thecen ter of the cells. e

,It. will'be evident that the..provision. of this opaque. barrierprovides important. advantages. .First, ifa. nar-, row beam of radiationis .used which would normally fall at a position within. the slot a,some deflection of the. beam, would occur .beforelit. fell uponvone orthe other of the photoelectric cells lfiaandithere Would, therefore, bean, insensitive region; or deadl space. where. changesin composition ofthe sample would not aficct the. output, of the instrument. Such aninactive zone' is clearly. avoided by provisionof thebarrier 30v andtheutilization of abroad radiation beamJ Second,.with the. systembalanceiand a region of equal Width ateach side ofthebarrier 30,. it isevident that substantially less radiationis incident upon. the detectorsthan wouldbe theicaselif a broadband were utilized. and the barrier 30omitted. The limitation of. the total radiation falling'upon. the.detectors,v in many. instances, permits them tobe operated at a moresensitive. and ad vantageous portion. of. their. characteristic. curve.

Finally, the. sensitivity. of the instrument is greatlyincreased'because: the higher beam. intensity in a narrow. band producesa, proportionately. higher 'outputin the detector when the beam isdeflected. The increase in sensitivitythus. obtained is quitesignificant in. practical.

operationjoff instrumentsof this type.

Inja practical ca'se, a 30-40% increase: in sensitivity was'obtainedf ina differenti'al refractometer. utilizing the opaque barrier oftheinvention. In this particular. instrument, the ribbons, of radiationwhich passed around the. edges, of thebarrier. were approximately inwidth, and the light intensity was considerably greater than wasprovidedv where a prism was used instead of the opaque barrier to causethe light to spread out over a large area of the photoelectricv cells.Thus, by the-present invention, an increasedusensitivity; andnbeamintensity, were obtained at.a.consid.erably, lower. costthan-inthe corr'sponding system where -a fprism.was used.. instead of the.

opaque barrier.

While the invention has :heenrdescri'bed in connection with present,preferred embodiments thereof, it isto be understood that .thisdescription is illustrative only and is not intended to limittheinvention.

I claim: V

1. In a photometric analyzer, in;combination, a rad ia-.

tion source, a reflector, a detector unithaving two radiation-sensitivedevices arranged in closely spaced formation, a cell assembly comprisingtwo cells each adapted to contain a fluid, means for directing radiationfrom said source through said cells to said reflector and, thence, to

said radiation-sensitive devices,.a circuit connecting the electricaloutputs of said devices in opposition to produce a voltagerepresentative of the difierence in intensity of radiation incident uponsaid devices, a cam,-a-'can1 follower engageable with said. cam andadapted torotate said reflector, a motor. for driving said cam, meansfor tween the potentiometer contactor and one fixedterminal thereof, anda'fixed barrier of. material opaquetosaid radiation mounted directly"infront of said'detector unit,. as related to the radiationimpingingthereon, said barrier intercepting the radiation directed. atthe area intermediate said radiatiomsensitive devices and a portionofneach lower e'nga'geable with said' cam and adaptedto rotate.

said reflector, a'motor. for driving. said cam, means for feeding saidvoltage to said motor, thereby to move. saidf cam and said reflectoruntil the radiationincident upon both devicesis of'equ'alintensity, anindicating device connected to said'rnotor to indicate the differencesin refrac-f tive-index between the'fluids in said cells, and a fixedbarrier of. material opaque to said. radiation mounted directly in'frontofjsaiddetector unit, as related to the radiation'impingin'gthereon, said barrier intercepting the radiation directed at the areaintermediate. said radiation-sensitive devices and' a portion of eachdevice .adjacentsaid intermediate area.

ReferencesCited' in the the of this'patent

